Maj-Gen Saad, appointed Aden governor in October after playing a prominent role in recapturing the city from Iranian-backed Houthi rebels in July, is reported assassinated in an explosion for which Daesh immediately claimed responsibility

The Sa'udi-led coalition has cleared the Huthis from most of lowland Yemen. With a disintegrating coalition, jihadis in their rear, they must now seize Yemen's mountains against dug-in foes. Or compromise at the peace talks.

James Spencer outlines the story so far

Having decided to prevent the Huthi  Salihi coalition from capturing Aden, the Sa'udi-led coalition intervened in Yemen with air attack. The hoped-for infantry from Pakistan, Egypt or possibly Turkey did not materialised. This caused a break in tempo while other ground forces had to be sought.

Meanwhile, after re-inforcing the Sa'udi-Yemeni border, the Sa'udi-led coalition began an air campaign against both Huthi-Salihi militias and the Zaydi civilian population, the latter presumably in the hope of breaking the civilians' will. Douhet's theory of air power has long been discreditted as a military campaign strategy; and so it proved. Tactically, airpower was of limited use due to the small and dispersed targets presented by the Huthis and Salihis. The main target - and casualty - has been Yemen's already limited infrastructure.

The blitz on the civilian population centres had a predictably jingoistic effect, butressing the Zaydi dogma of resistance to an unjust ruler. This foreign air assault, rather than drive an uprising against the Huthis, alienated even the Huthis' critics and former opponents from the Hashid tribal confederation.

Without foreign manoeuvre elements, the Sa'udi-led coalition began to train and equip Yemenis some near Little Aden, and some in Sa'udi Arabia. The Sa'udi-led coalition also air-dropped weapons and ammunition to anti-Huthi forces in Aden. From 12 July 15, a wave of Sa'udi-trained Yemenis in about 100 protected vehicles were landed in Aden, followed later by an Emirati armoured brigade. Backed by the Sa'udi-led coalition, the Yemenis  a mixture of Hadi-loyalists, secessionist Hirakis, and Sunni insurgents - quickly cleared the Huthis and Salihis present first from Aden, then Aden Airport, then al-Anad. Casualties were few, although the Emiratis lost a Special Forces officer in the fighting, and two armoued soldiers to anti-tank mines.

The coalition swept on to Ma'rib, linking up with fresh troops coming in from Sa'udi Arabia. They continued to push into the Southern Uplands towards Ta'iz, and along the coast towards Bab al-Mandab. In Ma'rib, a SCARAB missile strike on the Safer oil complex which was being used as a forward operating base, killed 45 Emiratis, 5 Bahrainis and 33 Yemenis, shocking the citizens of the Sa'udi-led coalition who had been lulled by the easy victories, and assurances that most such missiles had been destroyed.

After a pause, operations continued. In the West, Sa'udi-led coalition forces moved past Bab al-Mandab and up the Tihama. In the centre, Sa'udi-led coalition forces continued to press towards Ma'rib, and then on al-Jawf, squeezing the Huthi-Salihi forces between the Sa'udi border and advancing forces from the South. Having invested the mountains, the Coalition began to announce their intention to assault Sana'a, even promising to "purge Yemen of the scum".

From the beginning, there were demands by the Sa'udi-led coalition and the internationally recognised government for the full implementation of UNSCR 2216, and Huthi-Salihi counter-offers of discussions about a peace deal, with the former insisting on a maximalist position unacceptable to the Huthis and Salihis. Despite the efforts of the UN Special Envoy to coax all sides to talks, neither side has shown itself ready to accept the depth of compromise necessary to achieve a lasting peace; indeed both sides have taken too many casualties to compromise easily.

So what next?

The Sa'udi-led coalition has done the easy bit: the coastal areas and Ma'rib and al-Jawf are reasonably flat and open; easy for invading forces to take and occupy. That is the prime reason why the inhabitants are Sunnis. Yemen's mountain interior is like a castle, with towering walls, and few approaches. The coterminous location of the mountains and Zaydi tribes is no co-incidence: the mountains have enabled the tribes to resist attackers for centuries, and maintain their Zaydi identity.

The Sa'udi-led coalition have cleared the Huthis and Salihis from most of the former southern Yemen, and many Southern Secessionist Hirakis have no interest in what they regard as a foreign country: the North. Further, Salafi Jihadis are increasingly active in the Sa'udi-led coalition's rear areas, which will require troops to secure them.

As the Turks and Egyptians know, there are only a few avenues into the mountains from East or West. The Huthis and Salihis will have laid many mines in those passes. While one Explosively Formed Projectile was intercepted in 2012, it is likely that others  or at least the blue-prints  will have got through to the major arms dealer (possibly linked to the Huthis.) In addition to mines, the attacking forces will have to run the gauntlet of enfilade fire by EFPs: their optimised siting. While the media may describe the new vehicles as "armoured", in fact, many are merely "protected", like the infamous SNATCH landrover. Any Sa'udi-led coalition advance from a flank is thus likely to be very slow and very bloody.

To attack from the South is easier: the slopes are more gradual, and there are more approaches  although there are still choke-points such as the Samara Pass. But this approach from Ta'iz would involve fighting through the length of Zaydi territory, and even those tribes which had been against the Huthis have been been pounded by air power. That air power has degraded the infrastructure, making it difficult for the Sa'udi-led coalition to advance in their vehicles, while the Huthis will be able to exploit their own mobility, mines and EFPs. The Sa'udi-led Coalition may resort to contraversial equipment such as thermobaric devices  to "smoke out" the Huthis from caves, as they claim was done to their founder.

Each side appears to have gamed the situation: the Huthi-Salihis probably assess that many Sa'udi casualties will improve their negotiating position any peace conference. The Sa'udis - whose experiences in Yemen have been bruising  are aware of the likely high casualties, and have recruited Sudanese, Somali, Mauritanian and even Colombian soldiers, as the loyalty of their Yemeni tribal allies is unsure. This absence of a mutual relationship between the fighting soldiers and their commanders is likely to mean that the Sa'udi-led coalition casualty bill is higher than normal, as there is no societal brake on the commanders. When coupled with what many Huthis will regard as an existential threat to the Zaydi way of life, Huthi-Salihi casualties are likely to be many.

It is to be hoped that Yemeni good sense  and the UN  can prevail. If not, the next phase will be immensely bloody.

James Spencer is a retired infantry commander who specialised in low intensity conflict. He is a strategic analyst on political, security and trade issues of the Middle East and Africa and a specialist on Yemen

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